Tranny Downshift Problem (Overwind) - Diesel Truck Forum - TheDieselGarage.com
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post #1 of 6 (permalink) Old 07-01-2007, 07:48 PM Thread Starter
 
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Tranny Downshift Problem (Overwind)

HI everyone. I ma new to this forum but I can see I am going to spent lots of time here. I bought a used 05 Duramax. Truck had about 16000 miles on it. I have driven it about 2000 miles on it and love the diesel. However I towed with it for the first time this weekend. My travel trailer only weighs aobut 5500 loaded and the truck pulled in the mountains perfectly. On the way home coming down the hill when the tranny downshifted it went clear doen to 2nd gear I think and red lined the truck to 3500-4000 RPM. I could power through it but I really think I have a problem of some kind. I know the pryor owner towed a 32' fifth wheel with it. Is is possible that he had some tranny kit installed for the heavier trailer??? On some of the downhill it worked perfectly but three times it went over the top...Thanks for any help...

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post #2 of 6 (permalink) Old 07-01-2007, 10:30 PM
 
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Tractman,

The downshift is called grade-braking - it is perfectly normal for the Allison to downshift exactly as you describe. If you tap the gas pedal it will upshift again. The owners manual for the Allison states that the truck may redline when grade-braking and this is normal operation. Tow-Haul mode will do it more frequently, but it is always active (the grade braking feature.) I have had this happen when towing down mountains ....
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post #3 of 6 (permalink) Old 07-02-2007, 03:31 AM Thread Starter
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Thanks Cook, I looked at some FAQ on a GM site and it explained it just like it was happening. I was afraid I was overwinding the motor. I knew I was able to power through it but I was still concerned. THanks for the quick reply, I appreciate your help...

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post #4 of 6 (permalink) Old 07-02-2007, 01:08 PM
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you are not the only one who complained about it. The service departments were loaded with redline complaints. In 06 GM Finally relocated the redline placard on the rpm gauge.

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post #5 of 6 (permalink) Old 07-02-2007, 02:02 PM
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here is some information on the grade brake and how it works

http://www.kennedydiesel.com/allison_grade_braking.html

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post #6 of 6 (permalink) Old 07-05-2007, 12:59 AM
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just put it in tow hual mode and dont worry the allison trans is way smarter then any of us monitors tonns of inputs (speed sensors, throttle sensors etc etc, and decides what to do. itll take care of itself.

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